Chemical delivery devices produced using halftone screening in an additive manufacturing process

ABSTRACT

A method of forming a chemical delivery device with an active chemical includes generating halftoned image data using a stochastic halftone screen a concentration parameter for the active chemical. The method also includes ejecting a chemical carrier including the active chemical into a portion of a plurality of cavities formed in the chemical delivery device using the halftoned image data to produce the chemical delivery device with a concentration of the active chemical corresponding to the concentration parameter.

PRIORITY CLAIM

This application is a divisional application of and claims priority topending U.S. patent application Ser. No. 16/162,929, which is entitled“Chemical Delivery Devices Produced Using Halftone Screening In AnAdditive Manufacturing Process,” which was filed on Oct. 17, 2018, andwhich issued as U.S. Patent Number x,xxx,xxx on mm/dd/yyyy, the entiredisclosure of which is expressly incorporated in this document byreference, and that application is a divisional application of andclaims priority to U.S. patent application Ser. No. 15/294,676, which isentitled “System And Method For Additive Manufacture Of ChemicalDelivery Devices Using Halftone Screening,” which was filed on Oct. 14,2016, and which issued as U.S. Pat. No. 10,150,282 on Nov. 20, 2018, theentire disclosure of which is expressly incorporated in this document byreference.

TECHNICAL FIELD

This disclosure is directed to systems and methods of additivemanufacture and, more particularly, to systems and methods formanufacturing tablets or other items with substrates that providecontrolled release of a chemical using three-dimensional objectprinters.

BACKGROUND

Three-dimensional printing, also known as additive manufacturing, is aprocess of making a three-dimensional solid object from a digital modelof virtually any shape. Many three-dimensional printing technologies usean additive process in which an additive manufacturing device formssuccessive layers of the part on top of previously deposited layers.Some of these technologies use inkjet printing, where one or moreprintheads eject successive layers of material. Three-dimensionalprinting is distinguishable from traditional object-forming techniques,which mostly rely on the removal of material from a work piece by asubtractive process, such as cutting or drilling.

Additive manufacturing systems can produce a wide range of items withsome proposed uses including encapsulation of chemicals in solublesubstrates for the delivery of medications or more broadly to chemicaldelivery devices. The additive manufacturing system deposits an “activechemical” in the chemical delivery device that is suspended in anexcipient material of a substrate that dissolves in a solvent. As usedherein, the term “active chemical” refers to any chemical that isembedded within a chemical delivery device for controlled release overtime as the chemical delivery device dissolves in a solvent. As usedherein, the term “excipient material” refers to one or more types ofmaterial that form a structure of a chemical delivery device,encapsulate one or more active chemicals, and control the release of theactive chemicals within the chemical delivery device as the chemicaldelivery device dissolves in a solvent or melts in atemperature-controlled chemical release process. In many embodiments,the excipient materials are substantially non-reactive with the activechemical, but the excipient materials are soluble in some form ofsolvent that dissolves the chemical delivery device to emit the activechemical during use of the chemical delivery device. Excipient substratematerials are known to the art that dissolve in various solventsincluding water, acids, bases, polar and non-polar solvents, or anyother suitable solvent for different applications. Corn starch andmicrocrystalline cellulose are two examples of materials that arecommonly used as excipient materials for an active chemical ingredient,although other materials include gelatins, polymers, includingUV-curable polymers, and the like that are used in various chemicaldelivery devices. Some forms of excipient material dissolve to deliverthe active chemical by melting or otherwise disintegrating at anoperating temperature, such as an elevated melting temperature that ishigher than the typical ambient storage temperature for the chemicaldelivery device.

As the substrate dissolves, the active chemical releases into a mediumaround the chemical delivery device and produces a chemical reaction.Applications for such devices include, but are not limited to,medicament delivery in human and veterinary medicine, fertilizer andpesticide delivery for agriculture and horticulture, dye release fortracking the flow of water or other fluids, and delivery of an activechemical in an industrial process.

While prior art additive manufacturing systems can produce chemicaldelivery devices, some forms of chemical delivery devices requireadditional structural elements for proper operation. For example, sometime-release chemical delivery devices require a specific concentrationgradient of an active chemical to deliver a dose of the active chemicalthat varies over time. In some instances, the tablet does not deliverthe active chemical at a desired rate if the active chemical isdistributed within the volume of the tablet in a non-uniform manner. Forexample, the rate of release from the tablet can be too high at somepoints during the dissolving of the tablet when it delivers a largerconcentration of the active chemical than intended. Also, the rate ofrelease can be too low when the tablet delivers too low of aconcentration of the active chemical at particular point in time afterit is digested. Additionally, some tablets include two or more types ofactive chemicals that should not mix while in the tablet, but should mixonce the tablet dissolves. Consequently, improvements to additivemanufacturing processes and systems that enable production of tabletswith precise distributions of active chemicals would be beneficial.

SUMMARY

In one embodiment, a method of producing a chemical delivery device witha three-dimensional object printer has been developed. The methodincludes receiving with a controller a first concentration parameter fora first active chemical in a first region of a substrate in the chemicaldelivery device, generating with the controller halftoned image datausing a stochastic halftone screen and with reference to the firstconcentration parameter, the halftoned image data including a pluralityof activated pixels that correspond only to locations of a first portionof a plurality of cavities formed in a substrate that receive the firstactive chemical, and ejecting with at least a first ejector apredetermined amount of a first chemical carrier including the firstactive chemical into each cavity in the first portion of the cavities inthe substrate with reference to the halftoned image data to produce thechemical delivery device with a concentration of the first activechemical corresponding to the first concentration parameter.

In another embodiment, a three-dimensional object printer that isconfigured to produce a chemical delivery device has been developed. Thethree-dimensional object printer includes a support member, at least afirst ejector configured to eject a first chemical carrier including afirst active chemical toward the support member, and a controlleroperatively connected to the at least first ejector and a memory. Thecontroller is configured to receive a first concentration parameter fora first active chemical in a first region of a substrate in a chemicaldelivery device positioned on the support member, generate halftonedimage data using a stochastic halftone screen stored in the memory andwith reference to the first concentration parameter, the halftoned imagedata including a plurality of activated pixels that correspond only tolocations of a first portion of a plurality of cavities formed in asubstrate that receive the first active chemical, and operate the atleast first ejector to eject a predetermined amount of a first chemicalcarrier including the first active chemical into each cavity in thefirst portion of the cavities in the substrate with reference to thehalftoned image data to produce the chemical delivery device with aconcentration of the first active chemical corresponding to the firstconcentration parameter.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and other features of an additive manufacturingdevice or printer that produces chemical delivery devices including atleast one active chemical are explained in the following description,taken in connection with the accompanying drawings.

FIG. 1 is a diagram of a three-dimensional object printer that isconfigured to form chemical delivery devices.

FIG. 2 is a block diagram of a process for forming a chemical deliverydevice.

FIG. 3A is a plan view of cavities formed in one layer of a chemicaldelivery device where each cavity can receive an active chemical.

FIG. 3B is a first cross-sectional view of the chemical delivery deviceof FIG. 3A.

FIG. 3C is a second cross-sectional view of the chemical delivery deviceof FIG. 3A.

FIG. 4 is a depiction of concentration graphs for halftoned image datacorresponding to a distribution of an active chemical within a chemicaldelivery device.

FIG. 5 is a graph depicting a sample of a halftone screen and acorresponding arrangement of image data for two different activechemicals in a region of a substrate of a chemical delivery device.

DETAILED DESCRIPTION

For a general understanding of the environment for the device disclosedherein as well as the details for the device, reference is made to thedrawings. In the drawings, like reference numerals designate likeelements.

As used herein, the term “halftone screen” refers to a two-dimensionalor three-dimensional arrangement of numeric threshold values that areused to control a distribution of materials to form a three-dimensionalprinted object, such as a chemical delivery device. Each entry in thehalftone screen is referred to as a “dot” herein. The dots are arrangedin either a two-dimensional space for a two-dimensional halftone screenor a three-dimensional space for three-dimensional halftone screen. Theterm “dot center” refers to a single dot that serves as a centrallocation for a group of multiple dots that are each assigned a thresholdvalue based on the value of the dot center. For example, in someembodiments a controller generates a particular threshold value at a dotcenter and “grows” a set of dots with the same threshold value aroundthe dot center. In other configurations, a dot center corresponding to acavity that is a candidate to receive an active chemical is surroundedby “guard” dots that have a fixed value corresponding to excipientmaterial that encapsulates the cavity. The dot center corresponds to alocation in the halftone screen and the final image data that optionallyreceives an active chemical, based on the concentration parameter of theactive chemical and the value of the threshold in the dot center. Thesurrounding dots each correspond to locations that receive excipientmaterial and do not receive an active material to ensure that the activematerial is encapsulated within the chemical delivery device.

As described in more detail below, a printer uses the halftone screensin conjunction with concentration parameter data for one or more activechemicals to generate “halftoned image data” or more simply “imagedata”. The image data include two-dimensional or three-dimensionalarrangements of locations that specify a type of material in thechemical delivery device with each location in the image data beingreferred to as a “pixel” herein. Each pixel in the image datacorresponds to the location of one dot in a halftone screen. However,instead of the threshold values in the dots of the halftone screens, thepixels in the image data each include a value that specifies one type ofexcipient material or active material that the printer emits to form achemical delivery device with concentration levels of the activechemical that correspond to the concentration parameters. The term pixelas used herein also includes the ordinary meaning of the term “voxel”(volumetric-pixel) that refers to the three-dimensional volumetric unitsthat form the shape and structure of a model for a three-dimensionalprinted object. A three-dimensional object printer uses the image datato control the operation of ejectors or other material dispensers toform the structure and distribute the active chemicals in a chemicaldelivery device.

As used herein, the term “stochastic halftone screen” refers to ahalftone screen in which dot centers are uniformly sized andpseudo-randomly distributed throughout a two or three dimensional space.Traditional, fixed frequency halftone screens establish a set of dotcenters at fixed points, usually based on a crystalline lattice. Commonhalftone screens might place dot centers at the vertices of a square orhexagonal lattice in two dimensions (or at the vertices of cubes, or thecenters of close-packed spheres in three dimensions). A fixed frequencyhalftone screen increases the number of dots which are “on” by addingadditional dots next to an existing dot center. Stochastic screensincrease the number of dots that correspond to a particular thresholdvalue or range of threshold values by adding additional dot centers,which are generally not adjacent to a previous dot center.

As used herein, the term “vector halftone screen” refers to a type ofhalftone screen where a single halftone screen positions multiple typesof active chemicals in different locations to prevent mixing ofdifferent active chemicals during the manufacturing process of achemical delivery device. The vector halftone screen differs from manyprior art halftone screens that are associated with printed images whereeach color in a multi-color printer (e.g. a cyan, magenta, yellow,black) printer has a separate halftone screen and the printer generatesa separate set of image data for each color, which is often referred toas a “color separation”. In conventional printing, many printed imagesinclude halftoned image data in multiple color separations that printtwo colors of ink to the same physical location on a sheet of paper aspart of a printed image, which is sometimes desirable when printingcolor images. However, in many chemical delivery device embodiments,different active chemicals, which are analogous to different colors ofink, should not be printed in a single physical location since theactive chemicals should only mix upon being released from the chemicaldelivery device. By contrast, the vector halftone screens enable formingchemical delivery devices that employ multiple active chemicals, using asingle halftone screen that prevents multiple active chemicals frombeing printed to a single location.

Using the vector halftone screen, a controller assigns differentthreshold ranges to different active chemicals based on theconcentration parameter value of each active chemical. The thresholdranges do not overlap so that each dot center within the vector halftonecan be assigned to at most one type of active chemical or to anexcipient material for dots that do not correspond to any activechemical. At each dot location in the halftone screen, a controlleridentifies the threshold value in the halftone screen and generates apixel of image data that corresponds to at most one active chemicalbased on “stacked” threshold levels for one or more active chemicals.For halftone dots with threshold values that do not correspond to theranges for any active chemicals, the controller generates an image datapixel corresponding to an excipient material that fills the pixel.

As is described in more detail below in conjunction with FIG. 5 , onepractical embodiment of the halftone screen includes dots with an 8-bitnumeric range of threshold values (0-255). A controller receivesconcentration parameters, optionally as a percentage value, and assignsnon-overlapping or “stacked” portions of the 8-bit numeric range to eachconcentration parameter based on the size of the concentrationparameters (e.g. 25% for Chemical A→0 -63; 16% for Chemical B→64-104;and Excipient material for the remaining values 105→255). The controlleruses the dot values of the vector halftone screens at differentlocations to determine which compound is printed for each correspondingpixel in the image data by assigning each dot to one chemical based onthe value of the dot and the numeric ranges of each chemical (e.g. a dotvalue of 24→image data pixel for Chemical A; a dot value of 134→imagedata pixel for Excipient material). The statistical distribution ofthreshold values within the vector halftone screen ensures that multiplechemicals are distributed evenly within each region of the chemicaldelivery device. Thus, the vector halftone screen and correspondinghalftone process enables generation of image data that correspond to adistribution of one or more active chemicals that prevents mixing of theactive chemicals during the process of producing the chemical deliverydevice.

The terms “stochastic halftone screen” and “vector halftone screen” asused herein do not refer to mutually exclusive properties of halftonescreens. Instead, a single halftone screen can have both the t andvector properties described above that form a stochastic vector halftonescreen. For example, in a chemical delivery device that only uses asingle active chemical, a stochastic halftone screen enables productionof the chemical delivery device with a distribution of the single activechemical in different regions of the chemical delivery device based onconcentration parameters for the single active chemical in each of theregions. While the halftone screen in the single chemical configurationis optionally a vector halftone screen, the vector property is notrequired since there is only a single active chemical. In production ofchemical delivery devices that include two or more active chemicals, theprinter utilizes a halftone process with the stochastic vector halftonescreen to control the distribution of two or more active chemicalswithin the chemical delivery device.

As used herein, the term “process direction” refers to a direction ofmovement of a support member past one or more printheads during athree-dimensional object formation process. The support member holds thethree-dimensional object during the print process. In some embodiments,the support member is a planar member such as a metal plate, while inother embodiments the support member is a rotating cylindrical member ora member with another shape that supports the formation of an objectduring the three-dimensional object printing process. In someembodiments, the printheads remain stationary while the support memberand object moves past the printhead. In other embodiments, theprintheads move while the support member remains stationary. In stillother embodiments, both the printheads and the support member move.

As used herein, the term “cross-process direction” refers to a directionthat is perpendicular to the process direction and in the plane of thesupport member. The ejectors in two or more printheads are registered inthe cross-process direction to enable an array of printheads to formprinted patterns of an excipient material or active chemical materialover a two-dimensional planar region. During a three-dimensional objectprinting process, the printheads eject drops of the excipient materialto form successive layers of structure and cavities within a chemicaldelivery device.

As used herein, the term “z-axis” refers to an axis that isperpendicular to the process direction, the cross-process direction, andto the plane of the support member in a three-dimensional objectprinter. At the beginning of the three-dimensional object printingprocess, a separation along the z-axis refers to a distance ofseparation between the support member and the printheads that form thelayers of excipient material in a three-dimensional printed chemicaldelivery device. As the ejectors in the printheads form each layer ofexcipient material, the printer adjusts the z-axis separation betweenthe printheads and the uppermost layer to maintain a substantiallyconstant distance between the printheads and the uppermost layer of theobject during the printing operation. In some embodiments, the supportmember moves away from the printheads during the printing operation tomaintain the z-axis separation, while in other embodiments theprintheads move away from the partially printed object and supportmember to maintain the z-axis separation.

FIG. 1 depicts an additive manufacturing device embodied as athree-dimensional object printer 100, or more simply printer 100. Theprinter 100 is configured to operate printheads to form athree-dimensional printed chemical delivery device 300 that includes oneor more active chemicals encapsulated within a structure formed from atleast one type of excipient material. The printer 100 includes a supportmember 102, printhead arrays 104A-104C, 108A-108C, and 112A-112C, anultraviolet (UV) curing device 116, controller 128, memory 132, and aleveler 118. In the illustrative embodiment of FIG. 1 , thethree-dimensional object printer 100 is depicted during formation of athree-dimensional chemical delivery device 300 that is formed from aplurality of layers of excipient material. The chemical device 300includes multiple layers of cavities that receive active chemicals inthe form of drops of chemical carriers that one or more ejectors in theprinthead arrays 104A-104C and 108A-108C eject into portions of thecavities with reference to concentration parameters in different regionsof the chemical delivery device 300.

In the embodiment of FIG. 1 , the support member 102 is a planar member,such as a metal plate, that moves in a process direction P. Theprinthead arrays 104A-104C, 108A-108C, and 112A-112C, UV curing device116, and leveler 118 form a print zone 110. The member 102 carries anypreviously formed layers of excipient material along with cavities thathave been filled with an active chemical material through the print zone110 in the process direction P. During the printing operation, thesupport member 102 moves in a predetermined process direction path thatpasses the printheads multiple times to form successive layers of theexcipient material and active chemicals in the chemical delivery device300. In some embodiments, multiple members similar to the member 102pass the print zone 110 in a carousel or similar configuration. One ormore actuators move the member 102 through the print zone 110 in theprocess direction P. In the embodiment of FIG. 1 , an actuator alsomoves the support member 102 in the direction Z away from the componentsin the print zone 110 after each layer of excipient material is appliedto the support member 102 to form the chemical delivery device 300. Theactuator moves the support member 102 in the Z direction to maintain auniform separation between the uppermost layer of the chemical deliverydevice 300 and the components in the print zone 110.

Each of the printheads in the printhead arrays 104A-104C, 108A-108C, and112A-112C includes at least one ejector. In the illustrative printheadembodiments of FIG. 1 , each printhead includes a two-dimensional arrayof ejectors that eject drops of liquid using, for example, piezoelectricor thermal transducers. In many practical embodiments, each printheadincludes an ejector array with a density that enables printing ofseveral hundred or thousand drops of material per linear inch (DPI). Theprinter 100 depicted in FIG. 1 ejects drops of two different types ofactive chemical with the printhead array 104A-104C being configured toeject drops of a first active chemical and the printhead array 108A-108Cbeing configured to eject drops of the second active chemical. Theprinthead array 112A-112C ejects drops of an excipient material, such asa polymer material, which forms the structure of the chemical deliverydevice 300, including the cavities within the chemical delivery device300 that receive active chemicals.

In many embodiments, the active chemical is dissolved or suspended in achemical carrier for ejection as liquid drops through the inkjets in theprintheads 104A-104C and 108A-108C. In some configurations, the chemicalcarrier evaporates within the cavities of the chemical delivery device300 prior to sealing each cavity to leave the active chemical in thecavity, while in other embodiments the chemical carrier remains in aliquid state within the cavity. While the precise formulation of thechemical carrier can vary for different types of chemical deliverydevices, the chemical carrier is generally a liquid form of an excipientmaterial. That is to say, the chemical carrier does not interact withthe active chemicals or substantially change the nature of the chemicalreaction as the chemical delivery device dissolves and emits the activechemicals. Of course, some active chemicals are already available in aliquid form that is compatible with the printheads and ejectors in theprinter 100. In these configurations, the chemical carrier and theactive chemical are the same material.

While each of the printhead arrays 104A-104C, 108A-108C, and 112A-112Cis depicted as including three printheads, alternative configurationscan include fewer printheads or a greater number of printheads toaccommodate print zones with different sizes in the cross-processdirection. Alternative embodiments of the printer 100 include a greateror lesser number of printhead arrays to handle different combinations ofactive chemicals. While the printhead arrays 104A-104C, 108A-108C, and112A-112C remain stationary during operation in the printer 100,alternative printer embodiments include one or more printheads that movein the cross-process direction CP, process direction P, or in both thecross-process and process directions. The moving printheads form thestructure of a three-dimensional chemical delivery device and depositactive chemicals within the chemical delivery device. Additionally,while FIG. 1 depicts a single chemical delivery device 300 forillustrative purposes, in many practical embodiments the printer 100forms multiple chemical delivery devices simultaneously, such as a sheetof the excipient material containing multiple tablets that can beswallowed by an average human, using the printhead arrays depicted inFIG. 1 . The larger excipient material sheet is then mechanicallyseparated into individual chemical delivery devices after completion ofthe operation of the printer 100.

In the embodiment of the printer 100 shown in FIG. 1 , the printheads112A-112C act as a dispenser for the excipient material. In analternative configuration to the print zone 110, an excipient powderdispenser includes a spreader (not shown) that emits the excipientmaterial as a thin layer of powder that covers the upper surface of thechemical delivery device 300. The powder dispenser is positioned acrossthe print zone 110 in a similar configuration to the UV curing device116. The ejectors in the printheads 112A-112C eject drops of a liquidbinder material onto selected locations of each powder layer to bind andharden the powder into a durable portion of the chemical deliverydevice. The UV curing device 116 optionally cures the binder in someembodiments. The excess powder that does not receive the binder isremoved from the chemical delivery device 300 to expose cavities thatreceive the chemical carrier that includes the active chemicals from theprinthead arrays 104A-104C and 108A-108C.

In the printer 100, the UV curing device 116 is an ultraviolet lightsource that produces UV light across the print zone 110 in thecross-process direction CP. The UV light from the UV curing device 116hardens the excipient material on the uppermost layer of chemicaldelivery device 300 to form a durable portion of the chemical deliverydevice 300. The UV curing process solidifies the excipient material toaccept additional layers of excipient material and to form arrays ofcavities that can contain a liquid chemical carrier with an activechemical as ejected from the ejectors in one or more printhead arrays,such as the arrays 104A-104C and 108A-108C.

As use herein, the term “leveler” refers to a member that is configuredto engage the uppermost surface of each layer of the excipient materialin a chemical delivery device before the UV curing device 116 cures theexcipient material. In the printer 100, the leveler 118, which is alsoreferred to as a planarizer, applies pressure and optionally heat tosmooth the uppermost layer of excipient material in the chemicaldelivery device 300 and form a uniform surface that receives anadditional layer of the excipient material during a subsequent passthrough the print zone 110. In some embodiments, the leveler 118 is aroller coated with a low surface energy material to prevent adhesion ofthe excipient material in the chemical delivery device 300 to thesurface of the leveler 118. While the other components in the print zone110 remain at a predetermined distance in the Z direction from thechemical delivery device 300, the leveler 118 engages the chemicaldelivery device 300 during at least some passes through the print zone110 to smooth the uppermost layer of excipient material.

The controller 128 is a digital logic device such as a microprocessor,microcontroller, field programmable gate array (FPGA), applicationspecific integrated circuit (ASIC) or any other digital logic that isconfigured to operate the printer 100. In the printer 100, thecontroller 128 is operatively connected to one or more actuators thatcontrol the movement of the support member 102, the printhead arraysincluding the printhead arrays 104A-104C, 108A-108C, and 112A-112C, theUV curing device 116, and the leveler 118. The controller 128 is alsooperatively connected to a memory 132. In the embodiment of the printer100, the memory 132 includes volatile data storage devices such asrandom access memory (RAM) devices and non-volatile data storage devicessuch as solid-state data storage devices, magnetic disks, optical disks,or any other suitable data storage devices. The memory 132 storesprogrammed instructions 136 for the operation of the controller 128 tooperate components in the printer 100. The memory 132 also storeschemical delivery device structure data 138 that include athree-dimensional (3D) representation of the shape and structure of oneor more types of chemical delivery devices including specificarrangements of cavities within the chemical delivery devices. Thechemical delivery device structural data 138 include, for example, aplurality of two-dimensional image data patterns that correspond to eachlayer of excipient material that the printer 100 forms to produce thechemical delivery device 300. The memory 132 also stores concentrationparameters 140 that specify the concentration levels of at least oneactive chemical within one or more regions of the chemical deliverydevice 300. The memory 132 also stores one or more stochastic or vectorhalftone screens 142. As described in more detail below, the stochasticor vector halftone screens enable the printer 100 to control thedistribution of active chemicals to different portions of the cavitiesformed in the chemical delivery device 300. The controller 128 executesthe stored program instructions 136 to operate the components in theprinter 100 to form the three-dimensional structure of the excipientmaterial in the chemical delivery device 300. The controller 128 alsoexecutes the stored program instructions to generate halftoned imagedata and control ejection of drops of the active chemicals into portionsof the cavities formed in the chemical delivery device 300 based on theconcentration parameter data 140 and halftone screens 142 for differentregions of the chemical delivery device 300.

FIG. 2 depicts a process 200 for forming a chemical delivery device witha range of concentration levels for one or more active chemicals in asubstrate formed with one or more forms of excipient material. In thediscussion below, a reference to the process 200 performing an action orfunction refers to the operation of a controller in an additivemanufacturing device, such as a three-dimensional object printer, toexecute stored program instructions to perform the function or action inassociation with components in the additive manufacturing device. Theprocess 200 is described in conjunction with the three-dimensionalobject printer of FIG. 1 for illustrative purposes.

During process 200, the printer 100 optionally forms a substrate layerin the chemical delivery device from an excipient material with aplurality of exposed cavities that are available to receive an activechemical from the printer 100 during the process 200 (block 204). In oneembodiment, the printer 100 forms the substrate from a powderedexcipient material using a spreader that supplements the printheads112A-112C. The controller 128 operates ejectors in one group of theprintheads, such as the printheads 112A-112C, to eject a binder materialin a predetermined pattern to form a hardened layer of the excipientmaterial. The controller 128 operates the ejectors in the printheads112A-112C based on the chemical delivery device structure data 138 toform each layer of the chemical delivery device 300 with a predeterminedstructure and arrangement of cavities. The controller 128 also formscavities in the substrate in locations that do not receive the bindermaterial where excess powder that does not receive the binder is removedafter the printer 100 forms a layer of cavities. The printer 100generally forms each set of cavities from a plurality of layers of theexcipient material that form the floor and lateral walls of each cavity.

In another embodiment, one or more printhead arrays in the printer 100eject drops of the excipient material that harden to form the substrateand the cavities from multiple layers of the excipient material using,for example, a UV curable polymer or other suitable excipient material.The controller 128 uses the chemical delivery device structure data 138to control the ejection of drops of the excipient material from theprintheads 112A-112C to form layers of the chemical delivery device withthe predetermined shape and arrangement of cavities. In still anotherembodiment, a device other than the printer 100 forms the substrate andthe cavities. The printer 100 receives the substrate with exposedcavities on the support member 102.

FIG. 3A-FIG. 3C depict an example of a chemical delivery device 300 withmultiple layers of cavities. FIG. 3A depicts a plan view of thesubstrate in the chemical delivery device 300 with an array of cavities,such as cavity 324, formed in one layer of the chemical delivery device300. In the example of FIG. 3 the printer 100 is configured to generatehalftoned image data for an active chemical that is ejected into aportion of the cavities that are shown in FIG. 3A. In the illustrativeembodiment of FIG. 3A, the printer 100 receives different concentrationparameters for three different regions 304, 308, and 312 in the exposedlayer. While FIG. 3A depicts the regions 304-312 in one layer of thechemical delivery device 300, in many embodiments the regions extendthrough the cavities that are formed in multiple layers of the chemicaldelivery device 300 to form three-dimensional regions. Furthermore,while FIG. 3A depicts three regions 304-312 for illustrative purposes,alternative configurations can include a different number of regions andfurther include a gradient of varying concentration parametersthroughout the chemical delivery device 300.

FIG. 3B and FIG. 3C depict cross-sectional views of a portion of thechemical delivery device 300 taken along line 340. FIG. 3B depicts onelayer of exposed cavities including the cavity 324 where the exposedcavities are approximately hemispherical in shape to receive drops of aliquid chemical carrier and the active chemical. The chemical deliverydevice includes multiple layers of cavities in a three-dimensionalarrangement including the cavity 332. FIG. 3C depicts anotherconfiguration in which the excipient material that forms the upperlayer, including the cavity 324, by almost completely forming it with anopening at the top of each exposed cavity that is large enough to enablethe chemical carrier and active chemical to enter the cavities and tosubstantially fill the cavities. The excipient material in the chemicaldelivery device 300 seals the lower layers of cavities. In someembodiments, the printer 100 moves the support member 102 and chemicaldelivery device 300 through the print zone 110 multiple times to formthe structure of the chemical delivery device 300 from the excipientmaterial that provides a structure with multiple layers of cavities. Theprinter 100 ejects drops of the active chemical to fill a selectedportion of the exposed cavities in each layer of the chemical deliverydevice 300. The operation of the printer 100 to generate halftoned imagedata for different regions of the chemical delivery device 300 and ejecta chemical carrier including one or more active chemicals into differentsets of cavities using a stochastic halftone screen or a vector halftonescreen is presented in further detail below.

The excipient material that forms the structure of the chemical deliverydevice 300 isolates each of the cavities from each other to preventfluid communication between cavities. In particular, the excipientmaterial prevents the formation of fluid channels between cavities thatcould enable a larger than expected release of active chemical when theexcipient material dissolves to expose fluidly coupled cavities.Additionally, in chemical delivery devices that include two or moreactive chemicals, the isolated cavities prevent the active chemicalsfrom combining prior to the dissolution of the excipient material in thechemical delivery device 300. While FIG. 3B and FIG. 3C depict sphericalcavities, the chemical delivery device 300 can include cavities withdifferent sizes and shapes, including oblate spheroids and cylindricalcavities for different types of chemical delivery devices.

As depicted in FIG. 3A, the chemical delivery device 300 includesmultiple regions 304-312, and the printer 100 processes concentrationparameter data in multiple regions of the substrate to generatehalftoned image data that enable delivery of different densities of theactive chemicals to the cavities within each region. For example, in onechemical delivery device configuration, the concentration parametersincrease from the outermost region 304 through the intermediate region308 to the innermost region 312. Since the volume of each of the regionsdecreases from the exterior region 304 to the center region 312, aproper selection of concentration levels enables the chemical deliverydevice 300 to emit the active chemical at a substantially constant rateas the chemical delivery device 300 dissolves. Of course, in alternativeconfigurations the concentration parameters can affect the rate ofemission for the active chemical in a wide variety of ways including agradient that enables the chemical delivery device 300 to emit one ormore active chemicals at varying rates over time as the chemicaldelivery device 300 dissolves.

While the chemical delivery device 300 is formed with a cylindricalcenter with two hemispheres at each end of the cylinder in a shape thatis often associated with medication tablets and other chemical tablets,the printer 100 is configured to form the substrate with a wide varietyof shapes and sizes of the chemical delivery device and individualcavities. The chemical delivery device 300 is merely an illustrativeembodiment of a three-dimensional device with a plurality of layershaving cavities to receive various concentrations of an active chemical.

Referring again to FIG. 2 , the process 200 continues as the printer 100receives concentration parameter data that specify the concentrationslevels for one or more active chemicals in one or more regions of thechemical delivery device (block 208). The concentration parametersinclude a numeric value that specifies a proportion of the cavities in agiven region of the chemical delivery device that receive thecorresponding active chemical. In the printer 100, the controller 128receives stored concentration parameter data 140 from the memory 132.The concentration parameters correspond to one or more active chemicalswithin at least one region of the chemical delivery device 300. In oneembodiment, a concentration parameter for each active chemical isspecified as a percentage in a range of 0% to 100% where 0% indicatesthat the active chemical is absent from a particular region of thechemical delivery device, 100% indicates that all available cavities inthe region should receive the active chemical, and an intermediatepercentage that corresponds to a specific number of cavities in theregion that receive the chemical in the region. Some chemical deliverydevices include regions with concentration parameters for two or moreactive chemicals. The sum of the concentration parameters does notexceed 100% or some other predetermined maximum parameter value toensure that the substrate has sufficient cavity locations for all of theactive chemicals in the region of the chemical delivery device.

FIG. 4 depicts a graph 400 of concentration parameters for two differentactive chemicals (Chemical A and Chemical B) in different regions of achemical delivery device. In FIG. 4 a total of forty regions in athree-dimensional cylindrical volume approximates the shape of achemical delivery device, such as the device 300 of FIG. 3 . Each regioncorresponds to a three-dimensional concentric shell starting from aregion that surrounds the center of the cylinder (x-index 1) andextending to the exterior of the cylinder (x-index 40). The example ofFIG. 4 depicts concentration gradients for the two different activechemicals. As used herein, the term “concentration gradient” refers to achange in the concentration levels of the active chemical distributedthrough the different regions of the chemical delivery device that theprinter 100 produces based on a plurality of concentration parametersfor multiple regions in the chemical delivery device. The differentconcentration gradients enable different configurations of the chemicaldelivery device to emit the active chemicals at substantially constantrates, increasing or decreasing rates, or even oscillating rates as thechemical device dissolves.

In the example of FIG. 4 , the concentration gradient for the firstactive chemical A specifies a decreasing concentration from the centerof the chemical delivery device outwards towards the exterior of thedevice, while the concentration gradient for the second active chemicalB specifies an increasing concentration gradient from the center of thechemical delivery device outwards towards the exterior of the device.Alternative concentration gradients include a plurality of concentrationparameters that form non-linear and non-monotonic changes in theconcentration through different regions of the chemical delivery device.While FIG. 4 depicts concentration gradients over three-dimensionalregions in a chemical delivery device with an approximately cylindricalshape, similar concentration gradients are also applicable to chemicaldelivery devices with a wide range of shapes. Another approximation ofthe chemical delivery device 300 of FIG. 3A models the volume of thechemical delivery as a cylinder with two spheres: V=(4πr²+2πrh)δr.Similar approximations for the three-dimensional geometry of variouschemical delivery devices are known to those of ordinary skill in theart.

Referring again to FIG. 2 , the process 200 continues as the controller128 in the printer 100 generates halftoned image data using a stochastichalftone screen, (which may also be a vector halftone screen if multiplecompounds are being printed) with reference to the one or moreconcentration parameters in each region of the image data correspondingto the substrate (block 212). The controller 128 generates pixels ofimage data using the threshold values of corresponding dots in thehalftone screens and the threshold ranges of the active chemicals andexcipient materials based on the concentration parameters for one ormore active chemicals. As used herein, the term “activated pixel” refersto a pixel location in the halftoned image data that receives an activechemical, while the remaining pixels that form the structure of thechemical delivery device receive an inactive or excipient material. Inembodiments of the process 200 that form chemical delivery devices withtwo or more active chemicals, the controller 128 uses the vectorhalftone screen to generate image data with only one active chemical inany given pixel location of the image data. The printer 100 also ejectsdrops of excipient material for the remaining pixels that are notactivated pixels as is described in more detail below. The halftonedimage data include a plurality of activated pixels that correspond onlyto locations of a portion of a plurality of cavities formed in asubstrate that receive an active chemical. In some configurations, aregion receives one active chemical while in other configurations asingle region receives two or more active chemicals. As described above,the stochastic vector halftone screen includes an arrangement of dotswith threshold values that produces halftoned image data with adistribution of pixels that corresponds to the physical arrangement ofcavities in the chemical delivery device.

The halftone process generates the halftoned image data with apredetermined arrangement of pixels that corresponds to the locations ofcavities that are exposed in the substrate of the chemical deliverydevice. If the chemicals being dispensed do not have the samedissolution rate as the excipient material in the target solvent, or ifmultiple chemicals are included which must not touch, then the halftonescreen also includes “guard” dots with a predetermined threshold valueor range of values that surround the dots corresponding to differentcavities in the chemical delivery device. The guard dots have a fixedvalue that never corresponds to an active chemical. The printer 100generates the halftoned image data based on the guard dots that includescorresponding “guard” pixels that surround the locations of the cavitiesand that correspond to the locations of walls and other structures inthe substrate that do not receive drops of the active chemicals. In FIG.5 the halftone screen includes an arrangement of guard dots thatcorrespond to the arrangements of cavities in one layer of the chemicaldelivery device 300. The guard dots are assigned a predetermined valueor range of values (e.g., 255 in the example of FIG. 5 ) which ensuresthat they are only used for printing the excipient material, and not anyof the active chemicals.

To produce the halftone screens, the controller 128 either uses thepredetermined halftone screen data that are stored in the halftonescreen data 142 of the memory 132, or the controller 128 generatespseudo-random numeric threshold values for each dot that corresponds toa cavity and that is a candidate to receive an active chemical. Exceptfor situations where a region of the chemical delivery device issaturated to 100% concentration, only a portion of the cavities in eachregion receives an active chemical. The remaining cavities remain emptyor the printer 100 fills the empty cavities with either the excipientmaterial that forms the chemical delivery device 300 or an inactivematerial, such as water, glycerin, triglycerides, or another liquid. Thefill material depends upon the chemical properties of the environment inwhich the chemical device dissolves. In some embodiments, the chemicalcarrier that holds the active chemicals in solution also serves as aninactive liquid when ejectors in the printer eject the chemical carrierwithout any dissolved active chemical. The controller 128 uses athresholding process described below to identify the portions of thepixels that receive different active chemicals based on the halftonescreen dot values and the threshold ranges.

FIG. 5 depicts a two-dimensional halftone screen 500 corresponding to asingle layer of one region of a chemical delivery device that theprinter 100 uses during the process 200. The halftone screen 500 is anillustrative example of a stochastic t halftone screen that is suitablefor use in production of a chemical delivery device that incorporatesone or more active chemicals. In the printer 100 the memory 132 storesthe halftone screen 500 and optionally additional two-dimensional orthree-dimensional halftone screens with the halftone screen data 142.FIG. 5 also depicts a table 550 showing the concentration parameters fortwo different active chemicals that are distributed in the halftonedimage data. The halftoned screen data 500 are encoded in an 8-bitnumeric range where each dot takes on a value of 0 to 255, althoughother embodiments use different ranges and the guard dots could beassigned a different value, such as 0, in an alternative configuration.In FIG. 5 , the dots with values 255 are each guard dots that correspondto locations of walls or features other than cavities in the substrateof the chemical delivery device, and the printer 100 does not ejectdrops of active chemicals into the locations corresponding to guarddots. FIG. 5 depicts a single set of guard dots around each potentiallocation for the active chemicals, but alternative embodiments use adifferent number of guard dots based on the sizes and arrangements ofthe cavities in the substrate. Some embodiments omit guard dots ifseparation of the active chemical locations is not required for aparticular chemical delivery device. Additionally, while the halftonescreen 500 depicts a single dot for each cavity, different halftonescreen embodiments include dot arrangements for different sizes andshapes of cavities.

While FIG. 5 depicts the two-dimensional halftone screen 500 thatcorresponds to a region of a single layer of a larger three-dimensionalchemical delivery device, in the printer 100 the halftone screen data142 typically includes three-dimensional halftone screens that includemultiple layers to define a three-dimensional region of the chemicaldelivery device over multiple layers. Some layers of the halftone screenmay include only guard dots that correspond to the excipient material toenable the printer 100 to form protective layers of the excipientmaterial over previously filled cavities in the chemical deliverydevice. In a three-dimensional halftone screen embodiment, the halftonescreen 500 represents one layer in the multi-layer halftone screen.During operation, the printer 100 forms each layer of the chemicaldelivery device using one selected two-dimensional halftone screenportion of a larger three-dimensional halftone screen for each layer.

In one embodiment, the halftone screen is stored in the memory 132 priorto the printing process. As described below, the printer tiles a singlehalftone screen in a repetitive process to cover the three-dimensionalregion occupied by the chemical delivery device for a wide range ofchemical device shapes and sizes to enable a comparatively smallhalftone screen to be used to form the image data in one or more regionsof a larger chemical delivery device. The controller 128 adjusts thethreshold ranges that receive active chemicals based on theconcentration parameter data to enable the printer 100 to use a singlehalftone screen to produce image data and printed chemical deliverydevices with different chemical concentration gradients for one or moreactive chemicals in different regions of the chemical delivery device.In another embodiment, the controller 128 generates the halftone screenthreshold values during the printing process. The controller 128generates the numeric values in the dot centers of the screen in apseudo-random manner to produce a more uniform distribution than wouldbe achieved using completely random numbers. For example using apseudo-random process the controller 128 generates threshold values forthe dots where the probability of adjacent cavities having similarhalftone levels, which increases the likelihood that adjacent cavitiesreceive the same active chemical, is less than would be expected from apurely random process. In embodiments that use guard dots, thecontroller 128 only uses the pseudo-random process to produce thethreshold values for the dot centers that align with cavities in thechemical delivery device and the guard dots (e.g. dot values of 255 inFIG. 5 ) remain with fixed values.

During the process 200, the controller 128 generates activated pixelsfor one or more active chemicals in the portions of the halftoned imagedata based on the concentration parameters for each active chemicalwithin a region and based on the threshold values in the halftone screenthat are assigned to the dot locations for each cavity within theregion. As depicted in the table 550 the concentration parameter for afirst active chemical (Chemical A) is 32%, and the controller 128generates a threshold range of 0-81 (e.g. approximately 32% of 256available values) using the predetermined scale of 0-255 of FIG. 5 .Thus, the controller generates activated pixels in halftoned image datathat are assigned to the first active chemical corresponding to thelocations of dots in the halftoned screen 500 that have a numeric valueof 0-81. Table 550 includes another concentration parameter of 23% forthe second active chemical (Chemical B) and the controller 128 generatesa second numeric range of 82-140 (e.g. approximately 23% of the 256values with an offset of +82 to avoid overlap with the threshold rangeof the first chemical) for the second active chemical. The numericranges for the first active chemical and the second active chemical are“stacked” meaning that the numeric ranges do not overlap to ensure thatthe controller 128 selects at most one active chemical for any of thecandidate dots in the halftone screen (e.g., dots that do not have theguard value 255) in the image data 500. The remaining dots thatcorrespond to the cavities in the substrate with numeric dot thresholdvalues of 141 to 255 do not receive either of the first or second activechemicals and the controller 128 classifies these pixels as “inactive”in FIG. 5 , which indicates that the excipient material or anotherinactive material should fill cavities that do not receive the activechemicals.

For example, the halftone screen data 500 contains a dot 504 withnumeric threshold value 22. The controller 128 generates an activatedpixel for the first active chemical in the halftoned image data based onthe threshold value and the threshold range for the first activechemical based on the concentration parameter. Similarly, the controller128 generates an activated pixel for the second active chemicalcorresponding to the dot 508, which has the numeric threshold value 101.The controller 128 does not generate an activated pixel corresponding tothe dot 512 with numeric value 175 since the dot 512 does not fallwithin the threshold of either active chemical. Instead, the controller128 generates a pixel that is assigned to the excipient material oranother inactive material to fill the cavity that does not receive anactive chemical. Similarly, the controller generates image data pixelscorresponding to the excipient material for all of the guard dots withthe value 255.

In a multi-layer chemical delivery device, the printer 100 optionallygenerates or uses a pre-defined three-dimensional halftone screencorresponding to the three-dimensional arrangements of cavities inmultiple layers of the chemical delivery device. The three-dimensionalhalftone screen includes dot locations that are candidates to receiveactive material and guard dots in a similar configuration to thetwo-dimensional arrangement of dots shown in FIG. 5 . Three-dimensionalhalftone screens include multiple planes of dots similar to the planarscreen 500 of FIG. 5 that correspond to different layers of cavities inthe chemical delivery device. If the three-dimensional halftone screenis smaller than the object to be printed, the controller 128 tilesmultiple copies of the halftone screen, using a space-filling tilingprocess to produce a larger screen that completely encompasses thethree-dimensional volume of the chemical delivery device. Duringoperation, the printer 100 ejects drops of the active chemical orchemicals for an individual layer with a two-dimensional arrangement ofcavities with openings that are exposed to the printheads, such asprintheads 104A-104C and 108A-108C in the printer 100. Thus, while theprinter 100 generates three-dimensional halftoned image data in someembodiments, the printer 100 ejects the active materials into individuallayers of cavities in the chemical delivery device that are eacharranged in a two-dimensional layer.

In an alternative embodiment, the controller 128 further divides theregions in the three-dimensional chemical delivery device into a seriesof two-dimensional regions corresponding to each layer of cavitiesformed in the chemical delivery device. The controller 128 generates orloads from memory, 132, the halftone screen as a two-dimensionalarrangement of dots for each layer of cavities in the chemical deliverydevice based on the concentration parameters and gradients through thetwo-dimensional layer. Either embodiment of the process 200 enables theprinter 100 to form chemical delivery devices with varying distributionsof one or more active chemicals.

Referring again to FIG. 2 , the process 200 continues as the printeroperates at least one ejector to eject a predetermined amount of theactive chemical into each cavity in the portion of cavities in thesubstrate that corresponds to one of the activated pixels with referenceto the halftoned image data (block 216). Using the printer 100 as anexample, the controller 128 operates the ejectors in the printhead array104A-104C to fill each cavity in a first portion of cavities thatcorresponds to the locations of the activated pixels for the firstactive chemical in the halftoned image data. The ejectors in theprintheads 104A-104C eject a predetermined amount of the chemicalcarrier and the first active chemical into each cavity that correspondsto an activated pixel in the image data to ensure that each region ofthe chemical delivery device has a concentration of the active chemicalthat corresponds to the concentration parameter. In the printer 100, thecontroller 128 operates the ejectors in the printheads 108A-108C toeject the predetermined amount of the chemical carrier including thesecond active chemical into the second portion of cavities thatcorrespond to the activated pixels for the second active chemical in asimilar manner to the operation of the printheads 104A-104C. Using FIG.3A and FIG. 5 as examples, each of the activated pixels in the imagedata that the controller 128 generates using the halftone screen 500aligns with one cavity in the exposed layer of cavities in one region,such as the region 304, of the chemical delivery device 300. Theejectors in the printheads 104A-104C and 108A-108C eject a predeterminedamount of the chemical carrier and active chemicals into the cavitiesthat correspond to the first and second active chemicals, respectively,to form each region of the layer in the chemical delivery device 300with the appropriate concentrations of the active chemicals.

Process 200 continues as described above for any additional layers inthe chemical delivery device (block 220). The printer 100 appliesadditional layers of the excipient material to seal the exposed cavitiesin the chemical delivery device and encapsulate the active chemicals inany cavities that received the active chemicals, and forms another layerof cavities from the excipient material based on the chemical deliverydevice structural data 138 to form another layer of cavities in thechemical delivery device (block 224). In the illustrative embodiment ofFIG. 2 , the controller 128 repeats the processing described inconjunction with blocks 208-216 for an embodiment of the process 200that generates the activated pixels in the halftoned image data for eachlayer of the chemical delivery device individually. In anotherconfiguration, the process 200 repeats block 216 using previouslygenerated halftone data, such as another two-dimensional arrangement ofthe halftoned data in a larger set of three-dimensional halftoned data,to control the ejection of the active chemicals into the cavities of thenext layer of the chemical delivery device. Process 200 concludes whenno additional layers of cavities in the chemical delivery device remain(block 220) and the printer 100 seals the final layer of cavities withthe excipient material (block 228).

The printer 100 and process 200 enable additive manufacturing productionof chemical delivery devices that release one or more active chemicalsat varying rates and that incorporate multiple types of active chemicalmaterial with chemical isolation between the active chemicals until thechemical delivery device dissolves. The systems and methods describedherein enable production of chemical delivery devices with differentshapes and sizes with minimal reconfiguration of the three-dimensionalobject printer 100. Additionally, the printer 100 can produce chemicaldelivery devices with different operating characteristics merely byusing a different set of concentration parameters to adjust thedistribution of active chemicals throughout the structure of thechemical delivery device, or by using an alternate halftone screen.

It will be appreciated that variants of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be desirablycombined into many other different systems, applications or methods.Various presently unforeseen or unanticipated alternatives,modifications, variations or improvements may be subsequently made bythose skilled in the art that are also intended to be encompassed by thefollowing claims.

What is claimed:
 1. A method of producing a chemical delivery devicewith a three-dimensional object printer comprising: receiving with acontroller a first concentration parameter for a first active chemicalin a first region of a substrate in the chemical delivery device;generating with the controller halftoned image data using a stochastichalftone screen and with reference to the first concentration parameter,the halftoned image data including a plurality of activated pixels thatcorrespond only to locations of a first portion of a plurality ofcavities formed in a substrate that receive the first active chemical;and ejecting with at least a first ejector a predetermined amount of afirst chemical carrier including the first active chemical into eachcavity in the first portion of the cavities in the substrate withreference to the halftoned image data to produce the chemical deliverydevice with a concentration of the first active chemical correspondingto the first concentration parameter.
 2. The method of claim 1 furthercomprising: prior to ejecting the predetermined volume of the firstchemical carrier including the first active chemical, forming, with adispenser, the substrate from a plurality of layers including anexcipient material.
 3. The method of claim 2, the forming of thesubstrate further comprising: applying with a spreader a powderedexcipient material; and operating at least a second ejector to eject aliquid binder in a predetermined pattern to bind portions of theexcipient material to form the substrate.
 4. The method of claim 2, theforming of the substrate further comprising: operating at least a secondejector to eject liquid drops of the excipient material in apredetermined pattern to form the substrate.
 5. The method of claim 1further comprising: receiving with the controller a plurality ofconcentration parameters of the first active chemical for a plurality ofregions of the chemical delivery device; generating with the controllerthe halftoned image data using the stochastic halftone screen withreference to the plurality of concentration parameters; and ejectingwith the at least first ejector the predetermined amount of the firstchemical carrier including the first active chemical into the firstportion of the cavities in the substrate with a concentration gradientthrough the plurality of regions of the chemical delivery devicecorresponding to the plurality of concentration parameters.
 6. Themethod of claim 1 further comprising: receiving with the controller asecond concentration parameter for a second active chemical in the firstregion of the substrate in the chemical delivery device; generating withthe controller the halftoned image data using the stochastic halftonescreen with reference to the second concentration parameter, thehalftoned image data including a second plurality of activated pixelsthat correspond only to locations of a second portion of the pluralityof cavities formed in the substrate that receive the second activechemical, wherein the stochastic halftone screen further comprises astochastic vector halftone screen; and ejecting with at least a secondejector a predetermined amount of a second chemical carrier includingthe second active chemical into each cavity in the second portion of thecavities in the substrate with reference to the halftoned image data toproduce the chemical delivery device with a concentration of the secondactive chemical corresponding to the second concentration parameter. 7.The method of claim 6 wherein the controller generates the secondplurality of activated pixels only in locations of the halftoned imagedata corresponding to cavities in the substrate that do not correspondto any of the first plurality of activated pixels.
 8. The method ofclaim 1 further comprising: operating a dispenser to form excipientmaterial in any cavity in the plurality of cavities that does notreceive the first chemical carrier including the first active chemical.9. The method of claim 1 further comprising: after ejecting thepredetermined volume of the first chemical carrier including the firstactive chemical, forming, with a dispenser, a plurality of layers of anexcipient material over the substrate and the plurality of cavities tocover the plurality of cavities and to form another plurality ofcavities in another layer of the substrate of the chemical deliverydevice.
 10. An additive manufacturing process for a three-dimensional(3D) object printer comprising: assigning a numerical range thatcorresponds to each material percentage in a plurality of materialpercentages, each assigned numerical range does not overlap with thenumerical range assigned to any other material percentage; generatinghalftoned image data for a layer of an object to be formed by the 3Dobject printer using the assigned numerical ranges and a vector halftonescreen; and operating a plurality of dispensers using the generatedhalftone image data for the layer to distribute a plurality of materialsin the layer at non-overlapping locations within the layer in accordancewith the material percentages.
 11. The additive manufacturing process ofclaim 10 wherein each numerical range assigned to a material percentageis within a range of 0 to
 255. 12. The additive manufacturing process ofclaim 10 wherein the object being formed by the 3D object printer has aplurality of regions and each region has a different plurality ofmaterial percentages, the process further comprising: assigning to eachmaterial percentage within each region a numerical range that does notoverlap with the numerical range of any other material percentage withinthe region; generating halftoned image data for each region using theassigned numerical ranges and the vector halftone screen; and operatingthe plurality of dispensers using the generated halftone image data foreach region to distribute the plurality of materials in each region atnon-overlapping locations within the region in accordance with thematerial percentages for the region.
 13. The additive manufacturingprocess of claim 12, the operation of the plurality of the dispensersfurther comprising: operating at least one ejector to eject drops of afirst material.
 14. The additive manufacturing process of claim 13, theoperation of the at least one ejector further comprising: operating afirst ejector to eject drops of the first material; and operating asecond ejector to eject drops of a second material that is differentthan the first material.
 15. The additive manufacturing process of claim14, the operating of the plurality of dispensers further comprising:operating a powdered material dispenser to dispense a powdered materialthat is different than the first material and the second material. 16.The additive manufacturing process of claim 15 wherein the powderedmaterial is an excipient material.
 17. A method of making an object witha three-dimensional (3D) printer comprising: generating halftoned imagedata for each of a plurality of successive layers of the object using astochastic halftone screen, wherein for each of said successive layersthe halftoned image data includes (i) a plurality of activated pixelsthat correspond to locations in each successive layer that receive afirst material and (ii) a plurality of inactivated pixels thatcorrespond to locations in each successive layer that receive a secondmaterial that is different than the first material; and printing thesuccessive layers of the object using the generated halftoned imagedata.
 18. The method of claim 17 wherein the stochastic halftone screenis a vector halftone screen and the plurality of activated pixelscorrespond to locations in each successive layer that either receive afirst material or a third material, the third material being differentthan the first material and the second material.
 19. The method of claim17 further comprising: generating an activated pixel in the halftonedimage data in response to a value in the stochastic halftone screenbeing within a numerical range corresponding to a percentage for thefirst material.
 20. The method of claim 19 further comprising:generating an inactivated pixel in the halftoned image data in responseto a value in the stochastic halftone screen being within a numericalrange corresponding to a percentage for the second material.